They informed her of its worth as it was the gun the ruskies copied the ak 47 off of.
Yep. The STG-44 would have made the course of warfare a bit different if it had been introduced earlier. After the war, Schmeisser was either captured or defected to the Soviets (depending on who's to be believed), and production ceased. Two years later, Kalashnikov came out with a very
similar rifle in the AK-47. While there appears to be no proof that Schmeisser was behind the AK-47, the parallels and similarities are hard to miss.
Very few were brought into the United States, and I'm betting fewer were registered. I've only seen one in real life (and got to shoot it!), and the owner paid $36,000 for it.
However, if it wasn't registered in 1986, it's worthless. Worse, it's dangerous from a legal standpoint. That really chafes me, but it's beside the point. Theoretically, the only option is to turn it over to the BATFE and let them decide what to do.
Even if they do decide to send it to a museum, one can bet the internals will be gutted and it will be rendered nonfunctional.